Desalination process

ABSTRACT

A PROCESS OF DESALINATING WATER BY FORMING AN EMULSION COMPRISING DROPS OF SALT WATER COATED WITH SURFACTANT MEMBRANES, AND WASHING THE EMULSION TO R4ECOVER PERMEATEDPRODUCT WATER FROM THE SURFACE OF THE DROPS.! APROCESS FOR SEPARATING WATER FROM A SUBSTANCE SOLUBLE THERIN WHICH COMPRISES PASSING AN AQUEOUS SOLUTION OF SAID SUBSTANCE TOGETHER WITH AN OIL ANS ASURFACTANT INTO AN EMULSIFICATION ZONE, EMULSIFYING THE MIXTURE OF SAID AQUEOUS SOLUTION, OIL AND SURFACTANT WHEREBY DROPLETS OF SAID AQUEOUS SOLUTION ARE COATED WITH A WATER IMMISCIBLE MEMBRANE, SAID MEMBRANE BEING MORE PERMEABLE TO EITHER WATER OR THE WATER SOLUBLE SUBSTANCE THAN TO THE OTHER COMPNENT OF THE AQUEOUS SOLUTION, WASHING THE EMULSION WITH AN AQUEOUS SOLVENT PHASE WHEREBY THE MORE PERMEABLE COMPONENT PASSES THROUGH THE MEMBRANE INTO SAID SOLVENT PHASE AND AN AQUEOUS SOLUTION RICH IN THE LESS PERMEABLE COMPONENT REMAINS WITHIN SAID MEMBRANE, SEPARATING THE SOLVENT ROM THE EMULSION, BREAKING THE EMULSION COMPRISING SAID MEMBRANE AND SAID AQUEOUS SOLUTION RICH IN THE LESS PERMEABLE COMPONENT, AND RECOVERING A MIXTURE RICH IN THE MORE PERMEABLE COMPONENT FROM SAID AQUEOUS SOLVENT PHASE.

United States Patent Ofice Re. 28,002 Reissued Apr. 30, 1974 28,002DESALINATION PROCESS Norman N. Li, Edison, N.J., assignor to EssoResearch and Engineering Company No Drawing. Original No. 3,454,489,dated July 8, 1969, Ser. No. 552,198, May 23, 1966. Application forreissue June 9, 1971, Ser. No. 151,604

Int. Cl. B01d 13/00 U.S. Cl. 210-22 4 Claims Matter enclosed in heavybrackets appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE [A process of desalinating water by formingan emulsion comprising drops of salt water coated with surfactantmembranes, and washing the emulsion to recover permeated product waterfrom the surface of the drops] A process for separating water from asubstance soluble therein which comprises passing an aqueous solution ofsaid substance together with an oil and a surfactant into anemulsification zone, emulsifying the mixture of said aqueous solution,oil and surfactant whereby droplets of said aqueous solution are coatedwith a water immiscible membrane, said membrane being more permeable toeither water or the water soluble substance than to the other componentof the aqueous solution. washing the emulsion with an aqueous solventphase whereby the more permeable component passes through the membraneinto said solvent phase and an aqueous solution rich in the lesspermeable component remains within said membrane, separating the solventfrom the emulsion, breaking the emulsion comprising said membrane andsaid aqueous solution rich in the less permeable component, andrecovering a mixture rich in the more permeable component from saidaqueous solvent phase.

This invention pertain to a process for separating liquids fromsolution. More particularly, this invention pertains to a method forseparating salt or liquid from admixture with liquid. In its moreparticular form this invention pertains to the separation of salt fromliquid solutions particularly saline solution; saline solutions includebrackish waters, sea water, and, in general, salt solutions of any kindin which it is desired to separate salt from Water. The separation ofsalt from liquid or liquid from liquid is achieved by selectivepermeation through an oil-soluble liquid, surfactant membrane.

The problem of separating salt from liquid in which it is dissolved hasbeen present for many years. Recently, this problem has becomeincreasingly important because of a rapidly diminishing water supply.Thus, one ramification of the problem of separating salt from liquid,the separation of salt from sea water, has become perhaps the mostimportant problem under surveillance in the world today.

Other problems associated with the separation of salt from liquidincludes corrosion and large heat consumption.

A great variety of different methods have been utilized in an attempt toeffectively separate salt from sea water. Perhaps the greatest efi'ortin this area has been devoted to the growing of crystals within thesolution and then the subsequent separation of ice crystals from thesalt remaining in solution. Unfortunately, the crystallizationtechniques utilized have met with limited success. This is due mainly tothe fact that most techniques involve a sudden chilling of the solution.The sudden chilling, sometimes rcferrcd to as shock chilling, results inthe formation of crystals with an extremely wide particle sizedistribution. Many of the crystals are extremely small in size andalmost impossible to filter on an elfective largescale basis.

Additionally, the presence of the small crystals tend to blind anyfilters that are in use. Alternatively, it has been attempted toevaporate the liquid away from the salt and trap the liquid vapors foreventual recovery as a salt-free liquid. This technique looks somewhatpromising, but it does involve enormous expense. It will probablynecessitate an effective atomic power system and the expense involvedis, at present, prohibitive. Since the problems associated with thepresence of salt in liquid are acute, a more immediate solution isneeded.

According to this invention, the problems encountered in previousattempts to separate salt from solutions have now been solved. It hasunexpectedly been discovered that the separation of salt from solutions,particularly salt from sea water, with the resulting recovery of asubstantially salt-free fresh water can be accomplished by means ofselective permeation of one component of a salt-liquid mixture through aliquid surfactant membrane. Preferably, the surfactant-coated dropletsof the mixture to be separated are emulsified in order to enhance theseparation. The individual droplets of the mixture may first beemulsified and then coated, or the coated droplets may be emulsified;the latter technique is more desirable. However, either may be utilized.

In copending application Ser. No. 537,580, now U.S. Patent No.3,389,078, the problems of the prior art membranes were basicallysolved. In this application it was discovered that the separation ofmaterials, especially water and water-soluble solids and liquids whichmay be quite similar in their physical and/or chemical properties can beachieved by selective permeation through liquid membranes formed by oilsolutions of surfactant mole cules. Surfactants are surface activeagents having hydrophobic and hydrophilic ends. Although the use ofliquid surfactant membranes represents a significant improvement overthe prior art, this process was still faced with problems. The previoususe of liquid surfactant membranes resulted in some drop break up in thesolvent phase. This could be avoided by increasing the membranethickness, but this in turn would cut down on mass transfer. Animprovement on the process was made in Ser. No. 533,933, now U.S. PatentNo. 3,410,794, wherein an emulsion comprising droplets of a hydrocarbonmixture surrounded by a surfactant membrane is formed. The formation ofan emulsion of the surfactant coated droplets of the mixture to beseparated cuts down on the drop break up since the size of the dropletsin the mixture to be separated is reduced. Reduction of drop size leadsdirectly to a decrease of surface force responsible for membranerupture. This results in an increase in drop stability.

In addition, the rate of mass transfer is increased by utilizing apressure gradient. Emulsion droplets which range in size from l l0" cm.to l l0- cm. possess high internal pressure as a result of largecurvature effect. It can be shown that the difference between theinternal and external pressures is equal to twice the ratio of surfacetension to drop radius. Therefore, in the presence of surface forces, adecrease in drop size results directly in an increase of the internaland external pressure difference. (Ref. Surface Chemistry by L. I.Osipow, p. 11, Reinhold Publishing Corporation, New York (1962).)

Finally, the total large surface presented by these small dropletsresults in extremely efficient mass transfer, Reducing the drop radiusby half doubles the total surface area. In fact, the permeation rate ofthe more permeable component of a given mixture increases about 20 to 50times over the use of liquid surfactant membranes without the use ofemulsion.

The general advantages to be gained by the use of liquid membrane filmsover the solid polymeric films used in the past are numerous. Film lifeis extremely critical in selecting polymeric membranes whereas theproblem does not exist in liquid membranes. Unlike its solid statecounterpart, the liquid membrane is homogenous in composition and isfree of pinholes as a result of surface tension effect. Additionally,the solid membrane requires mechanical support; a liquid surfactantmembrane would not need a support.

The thinnest solid polymeric membrane which may be reasonably utilizedis about l inches thick. Whereas for a liquid membrane, which can be asingle molecular layer, the thickness may be in the order of 10" inches.Since permeation rate is inversely proportional to the film thickness,the use of a thinner membrane results in a far higher permeation rate.

Mass transfer rate per volume of equipment are also considerably higherbecause droplets have more interfacial area. The key to a successfulpermeation operation is the rate at which the liquid diffuses throughthe membrane utilized. If the rate is low, the process becomes tootime-consuming and is, therefore, ineffective. The instant process,which combines the numerous advantages outlined above associated withthe use of liquid surfactant membranes, with the additional advantagesof the emulsifying of the surfactant coated droplets of the mixture tobe separated, results in an extremely efficient separation process.

In more detail, the process of the instant invention concerns thediscovery that one may separate watersoluble liquids or salts fromsolution by means of a selective permeation through liquid membraneswhich are formed by oil-soluble surfactant molecules. As indicatedabove, this separation may be enhanced by emulsifying the droplets ofthe mixture before or after they are coated with the liquid surfactantmembrane. The emulsified droplets have a diameter of 10* cm. to 10- cm.,preferably 10 cm. to cm. The emulsification of the droplets may takeplace in any wellknown manner such as high speed mechanical stirring.

The individual droplets are coated with a liquid surfactant membranewhich allows either the salt or the liquid phase to permeate morerapidly. In some instances the salt will permeate at a greater rate thanthe liquid. This is most commonly found when using a strongly polarsurfactant. Examples of this are given further on in this specification.

In other instances, the liquid, which may be water, will permeate morerapidly than the salt. The rapid permeation of the liquid is encouragedby the compatibility of the membrane with water. As an example, thesurfactant used to make such liquid membranes can be Span, which isfatty acid esters of anhydro sorbitols condensed with ethylene oxide.

The emulsified droplets of solution, which are surfactant-coated, arethen washed with a solvent phase. The more permeable member or member ofthe solution will pass at a more rapid rate through the surfactantmembrane. It is preferred to have the more permeable member of themixture, whether salt or liquid, pass into the solvent phase whichcontinually washes the more permeable member away from thesurfactant-coated mixture. The more permeable member of the mixture,along with a relatively smaller amount of the less permeable member, isthen separated from the solvent by conventional means, such asdistillation. The less permeable member or members of the solution,along with a lesser amount of the more permeable member of the solution,are passed while still coated with the surfactant membrane to ademulsification zone, which may be an electrostatic coalescer. At thispoint the emulsion is broken and the less permeable compound, along witha small amount of the more permeable compound, is then separated fromthe oil surfactant solution. Generally, two separate layers are formedafter the demulsification which are the less permeable compound layerand the oil solution of surfactants. The former is taken out as productand the latter is sent to the emulsifier to be re-used.

It is within the scope of this invention to treat further the morepermeable and less permeable members of the mixture in order to obtain amore complete separation. Thus, several different separation zones maybe used in series in order to make the separation as distinct asdesired. In the case of desalinating water, using a series of 6 to 10separation zones, a separation which produces fresh water at a purity of98.5 to 99.0 may be obtained.

Any of the various oil-soluble surfactants may be utilized. However, ifone is desirous of having the salt permeate more readily than theliquid, it is preferred to use the surfactants with strong polarity. Ifit is more desirous to have the liquid pass through at a faster rate andthe salt remain concentrated within the surfactant membrane, one wouldutilize the surfactants with weak polarity and with high structuralcompatibility with the liquid permeate.

A wide variety of different surfactant groups may be utilized for theprocess of the instant invention. The various surfactant groups includelong-chain polar surfactants, fluorocarbon surfactants, silicones andmiscellaneous surfactants such as polymeric surfactants. All may beutilized in the process of the instant invention. Although for a givenseparation, one group may achieve greatly enhanced separation. Thepreferred grouping of surfactant to be utilized in the instant inventionare the surfactants with strong polar groups, since high polarity of thesurfactants aids in attracting permeates and therefore increasingtransfer rate. Typical polar groups are COOH, OH, NH CONH SH, -so,H, andsalts of long-chain carboxylic acids and sulfonates. The long-chainpolar surfactants include a wide range of compounds such as ethyleneglycol polyethers, polyethyleneoxy ethanol, phosphate radical onpolyethyleneoxy molecule. The latter is a weakly anionic surfactant.

Short-chain fluorocarbons with polar groups are frequently sufficientlysoluble in hydrocarbon oils to function as surfactants. Long-chainfluorocarbons attached to a hydrocarbon chain of sufficient length aresoluble in hydrocarbon oils.

Silicone oils differ broadly in their chemical structure andsurface-active properties. Those of sufficiently small molecular weightto be soluble in the hydrocarbon solvent and containing only CH groupsattached to silicon in the (Si- 0) skeleton can be expected to besurfaceactive.

The final overall grouping can best be called miscellaneous and includesa broad category of macromolecules and polymers such as fatty alcohols.

Since the number of surfactants is extremely large, it is not intendedto burden this application with numerous examples. The followingpublications are herein incorporated by reference. Surface Chemistry byLloyd 1. Osipow, Reinhold Publishing Company, New York (l962) chapter 8and Surface Activity, Moilliet et al., Van Nostrand Company, Inc. (1961)Part III.

Typical surfactants that may be utilized with this invention includeIgepal. This is a nonionic surfactant, nonylphenoxypolyethyleneoxyethanol. It is a trademark of the General Aniline and Film Corporationand has the configuration RC H O(CH CH O),,OH CH OH where R may be C lfC H or C l-I and n varies from 1.5 to 100. Igepals with n values up to 8are oil-soluble surfactants.

Span, a trademark of the Atlas Chemical Industries, is a series ofsurface active agents in the group of longchain polar surfactants. Spansare also known as sorbitan fatty acid esters because they are fatty acidesters of anhydro sorbitols condensed with ethylene oxide.

Cellulose acetate, a member of the group of macromolecules and polymersis one of the cellulose esters of the organic acids. By the action ofacetic anhydride on cotton in the presence of a little acid, celluloseacetate can be prepared. It has the formula and n will vary depending onthe conditions utilized.

Surfactant solution along with a suitable solution to be separated,i.e., salt water, is placed into a containing zone. Within this zone,the mixture is emulsified. This may be done in any of several ways suchas by high speed stirrers, colloid mills, valve homogenizers, ultrasonicgenerators, or mixing jets. The mixture can be emulsified prior to theaddition of the surfactant but it is preferred to add the surfactant andthen emulsify the mix ture. The preferred method of obtaining anemulsion is mixing the surfactant solution and the salt water for about1 to 5 minutes at speeds at 300 r.p.m. or higher. The surfactant coatsthe droplets of the salt water within the emulsion. These droplets areabout 1X10 to l X cm. in diameter. The emulsion is next passed into apermeation zone. Within the zone the surfactant coated droplets aregently washed with solvent. The more permeable member or members of thesolution pass out into the solvent phase. The solvent phase which isrich in the more permeable member of the mixture is then passed out ofthe permeation zone. The solvent phase is selected so that all membersof the solution are miscible to some degree with this phase. Themiscibility is preferred to be substantially similar for all thecomponents of the mixture since in this manner the separation isdependent on permeability through the surfactant membrane rather than asolvent extraction process. The solvent phase itself is preferablyaqueous in nature. Among the more eifective solvents that may beutilized for Washing the emulsion and separating the more permeablemember of the aqueous solution or mixture are water, alcohols andglycols.

As another alternative, multi-stages may be used to achieve additionalenrichment in the nonpermeating compound or compounds. It would beapparent that by using several stages of permeation a very fineseparation could be made of almost any solution no matter how close therelative rates of permeation are of the components of the mixture. Thus,after an initial separation the more permeable member or members of thesolution are separated from the solvent phase and may be recycled backto the original emulsion zone to be once again contacted with liquidsurfactant and a new emulsion formed. In the same manner after theemulsion has been broken the solution rich in less permeable compound orcompounds may be recycled back to the emulsion zone and treated again.This may continue as frequently as desired in order to producesubstantially pure compounds.

An extremely wide range of salt-containing liquids may be effectivelyseparated by the instant invention. This would include water containingsodium ion as well as other metal ions. Therefore, this instantinvention can effect desalination of seawater as well as extraction ofore or minerals from their aqueous solutions. Also, any liquid misciblewith water, such as alcohol in water, ketone in water, and acid. such asacetic acid, in water may be separated by this instant invention. Thisinstant invention is also an effective Way to separate azeotropicmixtures such as methyl ethyl ketone and water.

The following theory is offered for the operation of the instantinvention; there is no intent to be bound by any particular mechanism.The process of permeation of fluids through a liquid membrane may becomposed of three independent steps. Initially, a solution of thepermeating molecules maybe formed on the inside face of the liquidmembranes. Next, the molecules diffuse through the membrane. Finally,the molecules must be desorbed from the outside face of the membrane.Thus, among the factors which will effect the diffusion through a liquidmembrane are the membrane permeate compatibility, activity gradient andmembrane hole size.

A wide range of temperatures may be utilized in the process of theinstant invention. Temperatures used in the separation process itselfare not critical. There would, however, be a lower and an upper limitwhich would be satisfactory for separation with a liquid phasesurfactant membrane. The lowest temperature should be higher than thefreezing temperature of the surfactant solution. It will also have to behigher than the freezing temperature of the surfactant or of the aqueousmixture so that mass transfer will be facilitated.

In the event that nonionic surfactants are utilized, the highesttemperature should be lower than the precipitation temperature of thesurfactant. If an ionic surfactant is to be used, the highesttemperature is restricted by the boiling point of the surfactantsolution. Of course, the temperature will have to be lower than theboiling point of the aqueous feed or the solvent. Thus, the temperatureis to be regulated by the boiling point of the lowest boiling element inthe separation. It would be preferred to use room temperature sincethere is no additional expense in obtaining this level.

Pressure is also not critical and the most desirable pressure would beambient, i.e., one atmosphere. Sufficient pressure will be needed tomaintain all the elements of the separation, i.e., surfactant, solventand acqueous mixtures, in liquid phase.

The amount of surfactant to be added to the mixture which is to beseparated may also vary within wide ranges. 10- to 10* moles ofsurfactant may be added per liter of oil, preferably litto 10" moles ofsurfactant per liter of oil. It should be emphasized that liquidmembranes are utilized for the separation of liquid phase mixtures. Thesolvent phase must be miscible with the mixture to be separated. Thisprocess may also be utilized to separate mixtures of gases.

The solvents which may be utilized to wash the more permeable componentaway from the surfactant membrane are also quite varied in scope. Anyliquid which is miscible with the aqueous feed can be used. Thisincludes water, brackish water, ethylene glycol and its water-solublederivatives such as diethylene glycol monobutyl ether, alcohols such asisopropyl alcohol, ketones such as acetone and water-soluble acids andbases.

The selection of the solvent depends not only on its compatibility withthe permeates but also on the process economics.

The attached figure represents a schematic view of the separation schemeof the instant invention.

Turning to the figure, a mixture which may be any salt solution, but inthis instance is salt water containing about 4% by weight of salt isintroduced into emulsification zone 1, through line 2. A surfactant,which in this case would be Span 80, is introduced into theemulsification zone 1 through line 3. About l l0 to ix l0 moles ofsurfactant were added to the zone per mole of mixture to be separated.Within zone 1 an emulsion is formed by mixing the surfactant and saltsolution together at high speeds, speeds of 300 r.p.m. may be utilized.The surfactant coats the individual mixture droplets with a liquidcoating. The liquid-coated droplets have a maximum diameter roughly of0.0[ cm. and are passed through line 4 to solvent zone 5. Within thiszone the mixture is gently washed with solvent. Solvent is passed intothe solvent zone 5 through line 6. The washing of emulsion with solventis accomplished by mixing the emulsion with solvent at low speed; speedsof 10 to 100 r.p.m. may be utilized. In this particular instance, thesolvent is water and methyl ethyl ketone mixture. The washing periodtakes from 10 to 15 minutes and is conducted at a temperature of to F.ambient pressure. Solvent, along with the more permeable component,which in this case is water, passes out from the solvent zone 5 throughline 7 into separator zone 8, where the solvent is separated from themore permeable component. The solvent is separated within separator 8which in this case is a fractionator. The solvent is then recycled, ifdesired, back through line 6 into solvent zone 5. Product is removedthrough line 9; in this case the product is water. There will, ofcourse, be a minor amount of less permeable component present, but thismay be substantially removed by recycling.

An emulsion of surfactant and less permeable compound, with a minoramount of permeable compound still included, is removed through line 10of zone 5, passed into demulsification zone 11. The demulsification zonemay contain an electrostatic precipitator, but any of the well-knownmethods for breaking an emulsion may be utilized. Once the emulsion isbroken, the oil solution of surfactant and the less permeable compoundmay be readily separated. In this case the less permeable compound issodium chloride. The sodium chloride is removed through line 12 and theaqueous solution of surfactant is recycled through line 13 back toemulsification zone 1. The aqueous mixture is fed into emulsificationzone 1 at a rate of 100 to 1000 cc. per minute. Permeation rates, usingthe process of the instant invention, will vary between 10 and 1000gallons per hour per thousand square feet of membrane surface.

If cellulose acetate surfactant membranes are utilized, the salt willmore readily permeate through than the liquid.

When utilizing the following surfactants, the liquid will permeate morerapidly than the salt: fatty acid esters of anhydro sorbitols (Spans),polyphenoxy polyethyleneoxy ethanol (Igepals) and polyoxyethylated fattyacid.

Example 1 In this example, a process sequence similar to that in thefigure was utilized. A solution comprising salt water, which containedabout 4.0% salt, was introduced into emulsification zone 1 through line2. A surfactant which was a fatty acid ester of anhydro sorbitolsintroduced into zone 1 through line 3. About 190 grams of salt water wasused and about 230 grams of surfactant solution was added through line3. The surfactant solution and saline mixture were emulsified by meansof stirring. The saline solution was placed in the emulsifier first, andthen stirred at a speed of 300 r.p.m. The aqueous solution of surfactantwas then introduced gradually into the emulsifier. As a result, dropletsof 0.0l cm. and smaller diameter were formed, which were coated withsurfactant. Temperature for the mixing operation was 80 F. and pressurewas 1 atmosphere. After the emulsion was formed, the emulsified mixturewas passed through line 4 into solvent zone 5. Here the mixture wasgently washed with a solvent which was water with 6% ethylene glycol.Washing was done by mixing at a speed of 60 r.p.m. About 400 cc. ofsolvent was needed to wash the emulsion. The solvent was passed over themixture for a period of about 10 to 15 minutes. The compound whichpermeated more readily, which in this instance was water, together withabout 2.2 wt. percent of salt, was passed out of solvent zone 5, alongwith the solvent, through line 7, passed into separator 8, which was afractionator. Here the solvent was separated and recycled through line6. Product was obtained through line 9, which was water. The emulsionwas removed from solvent zone 5 through line 10. The emulsion was richin the less readily permeating compound, which was NaCl. It was thenpassed into electrostatic coalescer zone 11, wherein the emulsion wasbroken. Surfactant was removed through line 13 and recycled back intoemulsion zone 1. Product was recovered through line 12; this productcomprised water having 5.5 wt. percent of salt.

Example 2 In this example the exact conditions of Example 1 wereutilized, except that the surfactant was .1 wt. percent of celluloseacetate in grams of toluene and the solvent was water contining 2%acetone. Product was obtained through line 12, which was water having2.6 wt. percent of salt. The brackish water obtained from the separatorwas water having 4.8 wt. percent of salt.

What is claimed is:

1. A process for separating salt and water which comprises passing asalt solution and a surfactant into an emulsification zone, saidsurfactant being a nonpalar surfactant and having high structuralcompatibility with water, emulsifying said mixture wherein droplets ofsaid mixture are coated with a liquid surfactant membrane, said membranebeing more permeable to water than to salt, washing the emulsion with anaqueous solvent phase whereby a solution rich in salt remains withinsaid membrane, separating the solvent phase from the emulsion, breakingthe emulsion of said membrane and said solution rich in salt, andrecovering said water from said solvent phase.

2. The process of claim 1 wherein said surfactant is cellulose acetate.

3. The process of claim 1 wherein said water rich mixture is washed fromsaid surfactant coating with an aqueous solvent.

4. A process for separating water from a substance soluble therein whichcomprises passing an aqueous solution of said substance together with anoil and a surfactant into an emulsification zone, emulsifying themixture of said aqueous solution, oil and surfactant whereby droplets ofsaid aqueous solution are coated with a water immiscible membrane, saidmembrane being more permeable to either water or the water solublesubstance than to the other component of the aqueous solution, washingthe emulsion with an aqueous solvent phase whereby [an aqueous solutionrich in] the more permeable component passes through the membrane intosaid solvent phase and an aqueous solution rich in the less permeablecomponent remains within said membrane, separating the solvent from theemulsion, breaking the emulsion comprising said membrane and saidaqueous solution rich in the less permeable component, and recovering amixture rich in [water] the more permeable component from said aqueoussolvent phase.

References Cited The following references, cited by the Examiner, are

of record in the patented file of this patent or the original patent. M4UNITED STATES PATENTS US. Cl. X.R. 2l023

